@mixin transparent($color, $alpha)
  $rgba: rgba($color, $alpha)
  $ie-hex-str: ie-hex-str($rgba)
  background-color: transparent
  background-color: $rgba
  -ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorstr=#{$ie-hex-str},endColorstr=#{$ie-hex-str})"
  zoom: 1